1. Field Of The Invention
The invention relates to a transducer for reading information magnetically recorded on a magnetic storage medium. More particularly, the invention relates to a Faraday-effect magneto-optic transducer for providing an optical indication of magnetic states of the storage medium.
2. Description of the Prior Art
Magneto-optic transducers are known in the prior art for providing an optical indication of information recorded on a magnetic storage medium. A magneto-optic material is magnetized corresponding to magnetic fields produced by magnetization in an adjacent storage medium. A beam of polarized light irradiates the magneto-optic material which causes plus or minus rotation of the plane of polarization of the light depending upon the strength and direction of magnetization of the material. A light-responsive device detects these light variations, for providing an indication of the information recorded on the storage medium. The so-called Faraday effect occurs when light is transmitted through, rather than reflected from, a film of magnetized magneto-optic material.
U.S. Pat. No. 3,665,431 discloses a Faraday-effect transducer in which a magneto-optic film supported by a glass substrate, is positioned at an angle other than parallel with respect to an information-bearing surface of a magnetic tape. Because magnetization in a magnetic storage medium, such as magnetic tape, only induces magnetism in magneto-optic material a short distance from the storage medium, an edge of the magneto-optic film is in an essentially contacting relationship with the tape. To obtain high resolution and sufficient magneto-optic interaction, a polarized beam of light is focused on a minute portion of the periphery of the film adjacent the tape as the light is transmitted through the transducer.
In the transducer of U.S. Pat. No. 3,665,431, the light is transmitted through the glass substrate along an optical path which is oblique to the magneto-optic film. Polarized light is reflected at the interface between the film and supporting substrate as light enters and exits the magneto-optic film, thereby contributing to light loss as light is transmitted through the transducer. Additionally, because the refractive index of the glass substrate is different than the refractive index of the film, the light passing through the film is refracted both as it enters and exits the film. This refraction makes it more difficult to accurately align light-sensitive devices used to detect and analyze light transmitted through the transducer, as the angle at which light exits the transducer varies according to the thickness of the magneto-optic film and the angle of incidence of light impinging on the film.